-is the outer part of a magma body that
cools quicker because it is in contact with
the cooler
country
rock;
consequently grain sizes in the chill zone are smaller than
for the rest of the
magma
body.-chill
zone-Opal's Pals

cinders

-are small pyroclastic fragments of
vesicular basalt ejected from a volcano;
commonly about one
quarter inch to one
half inch in diameter.

-represent huge outpourings of fluid
basaltic lava which inundated a large
area of the Pacific
Northwest
of the
United States.

columnar jointing

-Upon cooling, igneous bodies shrink and
crack in a hexagonal pattern on
a horizontal plane;
these cracks
continue to
migrate downwards through
the cooling igneous body to create a
structure built
of six-sided columns.

crystal settling
-occurs within a magma chamber when crystals of a mineral form that are
denser
than the magma.
The denser crystals tend to sink to the bottom
of the magma chamber, removing
certain elements
and thereby changing
the composition of the magma.-crystal
settling-Opal's Pals

-is an intrusion, such as a dike, that cuts
across the grain or layering of
the pre-existing rock
(country rock).-dike
near Yuma, Arizona

dissolved gases

-Within a can or bottle of soda there a
significant amount of gas dissolved
within the fluid; without
it the soda
would
be flat. Similarly, there are many
varieties of gasses dissolved in magma which
are released when lava
erupts:
steam, carbon dioxide, sulfur dioxide,
hydrochloric acid, chlorine,
hydrofluoric acid, etc.

Flagstaff volcanics

-are located north of Flagstaff, Arizona;
the area has many cinder cones and
lava flows.

-Under the influence of gravity crystals
that form as as a magma cools either
settle to the bottom of
the magma
chamber
(dense compounds) or rise to the
roof of the magma chamber (low density
compounds).
-gravitational magmatic segregation-Opal's Pals

-is a hill-like structure made of viscous
magma, formed on top of a
composite volcano often
following a violent
explosive
event.
The present summit of Mt. St. Helens has one of these
structures
starting
to fill the gap where
the top of the volcano was blown off.

-occurs when magma from two or more
different sources come together
and mix underground.

magmatic differentiation

-is the process whereby the composition of a
magma changes as it cools
and newly crystallized
minerals
separate from the
magma.

magmatic stoping

-occurs when a magma body moves
upwards by cracking the ceiling rocks
by pressure and
allowing
fragments of the country
rock to fall into the
magma chamber. Stoping is a mining term
for mining
upwards.-magmatic
stoping-Opal's Pals

-is a silicic form of volcanism in which a
collapse crater is formed after
the explosive eruption of a
magma chamber that
has uplifted the surface
of the Earth. Magma production after the main
eruption
does not cease;
at a later time new magma domes the floor of the crater; in
other words
the surface
surges upwards again to provide the "re" in resurgent.-resurgent caldera and welded tuff lecture

-is a composite volcano made of alternating
layers of ash and lava; intermediate
in composition.
Many of the most famous
and prominent volcanoes in the
world are of this type: Mt. Fuji,
Mt. Rainier,
Mt. St. Helens, Mt. Shasta,
Mt. Kilimanjaro, Lassen Peak, etc.

-In a subduction zone, a slab of oceanic
crust with sediments is subducted
down into the hot mantle
where low temperature
minerals in the slab
start to melt. The newly formed magma rises to the
surface
adjacent to
the trench to produce volcanoes.
-subduction zone volcanics-Opal's Pals

sulfur dioxide

-is a poisonous gas given off by volcanoes.
Upon exposure to oxygen in
the air plus sunlight, sulfur
dioxide
turns into
sulfur trioxide that then
combines with moisture to form sulfuric acid and then
goes on to become
acid rain.-sulfur
dioxide-Opal's Pals

sulfuric acid

-is a powerful acid whose formula is
hydrogen sulfate.

Sunset crater, northern Arizona

-is a cinder cone north of Flagstaff,
Arizona. This small volcano is reported
to be the most recent
volcanic
eruption
in Arizona.
-Sunset Crater

tuff

-is an igneous rock consisting of compacted
volcanic fragments smaller
than one eighth of an inch.-tuff

Turkey Creek caldera, Cochise County,
Arizona

-is a large, eroded resurgent caldera in the
Chiricahua Mountains of
southeastern Arizona;
radiometrically
dated at 26
million years old.

-is an active volcano in Italy that is
responsible for destroying Pompeii and
Herculaneum.

viscosity

-is the measure of how resistant a fluid
material is to flowing.
For example, corn syrup is more viscous than water.
-viscosity-Opal's Pals

volcanic ash

-consists of very fine volcanic materials,
ranging from dust to particles less
than one eighth of an
inch.

volcanic bomb

-is a blob of lava ejected out of an active
volcano. As the material sails
through the air, the outer
surface of the
projectile cools and solidifies
before it hits the ground. Commonly, these
molten
blobs are spinning
as they
are ejected from the volcano and may develop
aerodynamic or
twisted
shapes.

-is a steep-sided, hill-like mass of viscous
lava extruded by a volcano; after
the explosive eruption
of Mt. St. Helens,
one
of these features slowly formed
in the newly created gap at the top of the
volcano; also called a lava dome.